The present invention relates to a secondary battery (hereinafter, simply referred to as a battery) evaluating method and a battery apparatus and in particular, to a method for evaluating remaining amount and service life of a battery mounted on a vehicle.
A lead battery is mounted as a secondary battery on a vehicle such as an automobile so as to serve as energy source for starting an engine, illumination, fuel injection device. In this case, it is necessary to accurately evaluate the remaining amount and service life of the lead battery. For example, after an engine is stopped, if there is no lead battery for supplying sufficient power for starting the engine next time, the engine cannot be started.
In general, the battery power is limited by a battery internal impedance. As the remaining amount decreases and the service life approaches its end, the internal impedance becomes larger. In order to maintain the engine start power, it is desired to accurately evaluate and control the battery remaining amount and service life.
Conventionally, there has been suggested a method for detecting a battery service life by measuring the internal impedance of the battery. JP-A-2001-235525 discloses a method for applying two types of AC current to a battery to measure an impedance and calculating the battery service life according to the measurement result.
[Document 1]
                JP-A-2001-235525 ([0045]–[0046], FIG. 7)        
In Document 1, the remaining amount is calculated by referencing the past judgment result. However, no consideration is taken on the affect of the change of the remaining amount as the time elapses, and if a comparatively large load such as an air conditioner is operated during idol stop, there arises a problem that the remaining amount cannot be followed. Moreover, since the internal impedance of the lead battery changes depending on the remaining amount, the service life calculated from impedance not considering the remaining amount lacks in reliability.
Moreover, in the case of a drive battery for a hybrid vehicle and fuel battery vehicle, the battery characteristic cannot be measured during running. Accordingly, there is a danger that there arise problems that power up cannot be performed during running or the engine cannot be started upon re-start.